The oxidative carbonylation of aromatic compounds to aromatic carboxylic acids is well known in the art. U.S. Pat. No. 3,700,729 discloses the catalytic liquid phase process comprising contacting an aromatic compound and carbon monoxide in a substantially anhydrous organic liquid reaction medium which is inert to the reactants and the catalyst which is a halide salt of a Group VIII metal in its highest oxidation state, continuing the contacting until the catalyst is reduced to a lower valence state and the aromatic compound is oxidatively carbonylated, and thereafter hydrolyzing the carbonylated compound to the aromatic carboxylic acid. The patent exemplifies the conversion of toluene to p-toluic acid. U.S. Pat. No. 3,920,734 discloses a process for preparing an aromatic carboxylic acid from an aromatic compound by means of carbon monoxide, oxygen and a palladium carboxylate catalyst. The patent exemplifies the conversion of toluene to a mixture of toluic acid isomers. U.S. Pat. No. 4,093,647 discloses a process for preparing an aromatic carboxylic acid from an aromatic compound of the benzene series by means of carbon monoxide and an inorganic salt mixture consisting of a major amount of a thallium salt and a minor amount of a palladium salt. The patent exemplifies the formation of a mixture of toluic acid isomers, predominantly the p-isomer, from toluene.
The acid-catalyzed carbonylation of aromatic compounds to form aldehydes is known in the art. Chem Systems, Inc., Process Evaluation and Research Planning Report, 2nd quarter, 1976, discloses the HF/BF.sub.3 catalyzed carbonylation of toluene to tolualdehyde which can be converted to terephthalic acid by a liquid phase oxidation. A similar disclosure as to the formation of tolualdehyde is made in British Pat. No. 1,485,816. Japanese Publication No. J5 1146-430 based on Japanese Patent application No. 070587 discloses the formation of tolualdehyde from the reaction of toluene and carbon monoxide in the presence of trifluoromethanesulfonic acid (often referred to as triflic acid) in an anhydrous state or in combination with a Lewis acid.
It is an object of this invention to provide a catalytic liquid phase process for producing toluic acids from toluene. A further object is to provide such a process whereby at least 50 mol % of the toluic acids produced is p-toluic acid. Other objects will become apparent hereinafter.